During the next year we hope to characterize ecdysone binding proteins present in an embryonic cell line (Kc) established from Drosophila. The cell line has a defined response to beta-ecdysone. A similar response can be induced by alpha-ecdysone at a 100-fold increase in concentration. In addition, the cells do not metabolize ecdysone to a discernable extent. Characterization of the macromolecular binding components by conventional physical techniques will permit elucidation of the mechanism whereby ecdysone interacts with the Drosophila genome.